Acoustical apparatus



Jan. 4, 1949.

3 Sheets-Sheet 1 Filed Aug. 29, 1942 Bnventor KMANN Gttomeg 1949- J. E.VOLKMANN ACOUSTICAL APPARATUS 3 SheetsSheet 2 Filed Aug. 29, 1942 4Summer JOHN E. MILK/v N (Ittorneg J. E. VOLKMANN ACOUSTICAL APPARATUSJan. 4, 1949.

5 Shee ts-Sheet 5 Filed Aug. 29, 1942 JOHN I 1 0mm??? (Ittorncg PatentedJan. 4, 1949 ACOUSTICAL APPARATUS John E. Volkmann, Indianapolis, Ind.,assignor to Radio Corporation of America, a corporation of DelawareApplication August 29, 1942, Serial No. 456,627

'1 Claims. 1

This invention relates to acoustical apparatus, and more particularly tohorn structures for auditorium loud speakers.

It is well known that sound reproduction in the average auditorium ortheatre calls for the use of directional loud speakers which give a highratio of direct to reflected sounds if a high degree of intelligibilityis to be obtained. In the early days of sound motion pictures and othersimilar types of reproduction, the directional loud speakers employedwere not uniformly directional with frequency, being more directional atthe high frequencies, with consequent distortion in the frequencybalance at the seats located on the sides of the front rows. In thedevelopment of the art, cellular high frequency loud speakers were laterprovided which givea more uniform characteristic and overcome the lackof coverage at the side seats in the front of the auditorium. Whilegiving adequate spread for the front seats, the cellular loud speakerarrangement has too great a spread for the more remote seats, with theconsequent result of directing too much sound energy to the side wallsfrom which reflections are obtained. In addition, due to theapproximately spherical distribution pattern of the cellular loudspeaker arrangement, the remote seats suffer some loss in sound level ascompared to the front seats.

The primary object of my present invention is to provide an improvedhorn structure for auditorium loud speakers which will not be subject tothe aforementioned disadvantages.

More particularly, it is an object of, my present invention to providean improved horn structure for loud speakers which will have improveddistribution characteristics.

Another object of my present invention is to provide an improved hornstructure for auditorium loud speakers which will radiate its energydirectly to and uniformly for all parts of the auditorium and with theleast waste due to sound radiating beyond the confines of the seatingarea which, indoors, usually gives rise to unnecessary reflections.

Still another object of my present invention is to provide an improvedhorn structure for auditorium loud speakers the directional pattern ofwhich can be fitted to the distribution requirements of the auditoriumor other seating area or space in which it is to be used.

It is also an object of my present invention to provide an improved hornloud speaker as aforesaid Which is relatively simple in construction andhighly efficient in use.

In accordance with my present invention, I

provide a horn structure comprising a plurality of horns, or rows ofhorns, each associated particularly with a preselected seating area ofthe auditorium, and each of which is arranged to have a distributionangle corresponding to the angle subtended at the loud speaker by thevarious rows of seats or seated areas of the auditorium with which eachhorn row is associated. The several horns or rows of horns, as the casemay be, are

contiguous to each other to prevent phase shift and are so arranged thatenergy per unit area at the seats is made uniform for the entire seatingarrangement, the ratio of direct to reflected sounds being maximum sinceall of the radiated energy is directed to the seats before reaching theWalls. Such a distribution characteristic can be very nearlyapproximated by stacking several horns in a plurality of rows or layersin pyramid fashion such that the distribution angle of each layercorresponds to the average distribution required by the area towhich'the energy is radiated, it being assumed that the energy fed intothe throat of each. horn layer is either equal, or preferably inproportion to the respective areas covered by each horn layer. Each rowor layer of the pyramida1 arrangement consists of one or more hornsarranged to provide approximately a radially expanding cylindrical Wavefront, and each row or layer of horns covers a different, preselectedarea of the auditorium.

In one form of my present invention, the pyramid horn may be of cellularconstruction with an appropriate number of individual cells or horns ineach row, the number of cells in each row decreasing in an upwarddirection and the individual horns all facing in a slightly differentdirection so chosen as to provide a cylindrical wave front for eachlayer of horn cells or approximately a spherical wave front for theaggregate of horns. The distribution angles of the several horn layersare such that a progressively sharper angle of distribution is obtainedfrom the lowermost to the uppermost layer.

In another and preferred form of my invention, a single horn is providedfor each row or layer, each of the horns again expanding radially togive a cylindrical wave front and preferably having the same rate offlare, the same throat area, and the same mouth area. However, the angleof flare and the aspect ratio (that is, the ratio of width to height) ofthe mouth area of each horn differ in each case in a manner to providehorizontal and vertical distribution angles for the respective hornswhich are progressively sharper as the uppermost horn is approached.With this form of my invention, a wide distribution pattern is obtainedsuch as may be obtained by the use of a cellular or diffuserconstruction, but without the inherent disadvantages of the cellularconstruction referred to hereinafter in greater detail. With either formof my invention, the directional pattern of the loud speaker may becustom fitted, so to speak, to the distribution requirements of theauditorium or other space in which it is to be used, or to someparticular area thereof which is to be covered. This may be accomplishedeither (a) by a suitable combination of horns and/or driving units, (b)by positional (that is, phase) adjustment of the horns and/or units, or(c) by a combination of both (a) and (b).

The novel features that I consider character istic of my invention areset forth with particularity in the appended claims. The inventionitself, however, both as to its organization and method of operation, aswell as additional objects and advantages thereof will best beunderstood from the following description, when read in connection withthe accompanying drawings in which Figures 1 and 2 are diagrammatic topplan and side views of an auditorium with reference to which theprinciples involved in the present invention are explained hereinafter,

Figure 3 is a top plan view of one form of loud speaker horn structureconstructed in accordance with my present invention,

Figure 4 is a front elevation thereof,

Figure 5 is a side elevation thereof,

Figure 6 is a front elevation of another form of horn structureconstructed in accordance with my present invention,

Figure 7 is a top plan view of the latter form of my invention,

Figure 8 is a central sectional view of the latter form of my inventiontaken on the line VIII-VIII of Figure '7, and

. Fig. 9 is a view similar to Fig. 8, but only partly in section, andshowing a somewhat different form of horn structure constructed inaccordance with my present invention.

Referring more particularly to the drawings, there is shown, inFigures 1and 2, an auditorium I, such as a theater having an orchestra 3, abalcony 5 and stage 1 at one end above which may be located a movingpicture screen or the like 9. Behind the screen 915 a loud speaker Hconstructed in accordance with my present invention and'described ingreater detail hereinafter.

From an inspection of Figure 1, it will be evident that, in order tocover all of the seats in the front portion of the orchestra 3, that is,the seats in the vicinity of the stage I, it is necessary that the loudspeaker II should have a relatively wide horizontal angle ofdistribution A1. If the loud speaker H were to distribute sound overonly the angle A1, it is obvious that the seats in the rear of theorchestra and in the balcony would receive a considerable quantity ofsound reflected from the walls of the auditorium instead of receivingmostly direct sound, as would the front seats in the orchestra. If,however, the loud speaker II can be made to cover different portions orareas of the auditorium in each of which the seats would receive directsound, improved results will be obtained. This can be accomplished byproviding a loud speaker which will have a different angle ofdistribution to various parts of the auditorium, as represented by thehorizontal angles A2 and As, the angle A2 embracthe uppermost row I6.

ing approximately the mid-portion of the auditorium and the angle membracing the rear of the auditorium. Thus, it will be seen that theangles A1, A2, and A3 are progressively smaller in the order named.

In a vertical direction, it is also desirable to have the loud speaker II distribute the sound directly to and uniformly over all parts of theauditorium. This may be accomplished by having various portions of theloud speaker radiate the sound over various distribution angles whichcover various areas, such as those embraced within the vertical anglesB1, B2, and B3 in Figure 2. Here, again, the angles Bl, B2 and B3 areprogressively smaller in the order named, the angle B1 embracing thefront part of the orchestra, the angle B: embracing the rear part of theorchestra (and, if necessary, the front part of the balcony as well) andthe angle B; embracing the balcony, or at least the rear portion thereofif the angle B2 also embraces the front portion of the balcony.

One form of loud speaker which will accomplish the foregoing results isshown in Figures 3, 4 and 5. This comprises a plurality of contiguousrows l2, I4 and I6 of individual horns l'l stacked on each other inpyramid fashion, as clearly seen in the drawings. The horns ll all havethe same rate of flare, the same mouth area, the same throat area, andthe same length, and each has, individually, the same angle of flare.Depending on the requirements of the particular auditorium where thehorn structure is to be used and on the position of the horns, there maybe provided one or more individual horns ll (public address and soundreenforcing loudspeakers are usually overhead or to the sides of theproscenium) in each of the rows l2, l4 and IS, the horns I? eachconstituting a cell of the horn structure. The axes of the individualhorns are angularly related to each other, as is best evident fromFigure 4, and the horns are so arranged as to provide approximately aradially expanding wave front. Each layer or row of horns expandsradially in a horizontal direction only, so that the wave front providedthereby expands cylindrically. However, the several rows may expandsubstantially radially in a vertical direction as well, in which casethe wave front could be considered as expanding spherically. In anycase, the greatest number of horns will normally be in the lowermost rowl2 and the smallest number of horns will be in the uppermost row l6.Thus, it is apparent that the several horn rows have differentdistribution angles which are progressively smaller or sharper from thelowermost row l2 to The several horn layers I2, l4 and It may beenclosed within a suitable casing IS the back of which carries one ormore throats II by means of which the several horns l1 may be connectedto a single driver 23. Any suitable combination of drivers and throatcouplings may, however, be used.

The horn row [2 is directed downwardly and embraces the angle Bl. Sincethis row requires the widest side-to-side or horizontal distributionangle A1, it is provided with the greatest number of horns. It isobvious that the horn row 11 will therefore cover the front rows of theorchestra adequately and will radiate direct sound thereto. In the rowI4, the horns I! are so arranged that they will radiate sound directlyto the rear portion of the orchestra. Since this row need only embracethe angle A2 from side to side, a smaller number of horns suflicestherefor. The smallest horn row l6 embraces the smallest horizontal dis-The form of my invention just previouslydescribed is open to theobjection that the energy radiated by each horn row or layer isproportional to the number of its cells. Consequently, the top layer I6may not radiate sufificient energy for the remote seating areas in therear portion of the balcony. To overcome this objection, the form of myinvention shown in Figures 6, '7 and 8 may be employed. In this form,each horn layer is constituted by a single discrete horn, thelowermosthorn 3i having the greatest angle of distribution from side to side, theintermediate horn 33 having a relatively smaller, angle of distributionfrom side to side, and the topmost horn 35 having the smallest angle ofdistribution from side to side. Here, again, the horns 3|, 33 and 35 arecontiguous to each other to prevent phase shift and are stacked on eachother in pyramid fashion, The three horns 3|, 33 and 35 face indifferent directions, the horns being so related to each other that whenthe horn 3| faces downwardly, the horn 33 faces forwardly, and the horn35 faces upwardly. In each of the horns 3|, 33 and 35, the rate of flareis substantially the same, as are also the areas of the throats andmouths of the respective horns. A single throat member 31 may beconnected to the throat ends of the horns 3|, 33 and 35 and connectsthese horns to one or more suitable drivers 39, only one driver beingshown in Fig. 8 for the sake of illustration.

Each of the horns 3|, 33 and 35 is constructed to provide a radiallyexpanding wave front from side to side. However, the angle of flare ofeach of the horns in this modification differs, as does also the aspectratio of their mouth areas, that is, the ratio of the width to theheight of the mouth. By suitably proportioning the mouths of the horns,appropriate horizontal and vertical angles may be obtained which areprogressively sharper from the lowermost horn 3| to the uppermost horn35. It will be noted, from an inspection of Figure 8, that the axes ofthe horns 3| 33 and 35 are angularly related to each other in a common,vertical plane. It will also be noted that the angle X between the axesof the horns 3| and 33 is greater than the angle Y between the axes ofthe horns 33 and 35. These axes may be so located as to provide thecoverage for predetermined areas of the auditorium. In one construction,for example, the angle X was approximately degrees and the angle Y wasapproximately degrees, the horn structure having had an overall lengthof 23 inches from the mouth of the horn 33 to the rear end of the throatmember 31. In the same construction, the horn 3| had a horizontal spreadof 120 degrees, and its mouth was four and a half inches high; the horn33 had a spread of 90 degrees, and its mouth had a height of 6 inches;and the horn 35 had a horizontal spread of 60 degrees, and its mouth hada height of 9 inches. The initial throat area of each horn was one inchhigh by four inches wide.

Since the directional characteristics of an aggregate of horns atcertain frequencies, especially the lowerand mid-range frequencies,depends not only on the directional properties of the individual hornsbut on the amplitude and phase relations between the horns as well, thedirectional pattern of the loud speakers herein described can becontrolled somewhat by adjusting the lateral and vertical position ofthe horns relative to each other, as well as by their angular position.Also, with the horns fixed in position, some adjustment of the wavefront -(and hence the directional pattern of the wave leaving the loudspeaker) can be .obtained by adjusting the phase relation between thedriving units, either by acoustical means (spacing, path length, etc.)or by suitable electrical means.

Although I have shown and described two embodiments of my invention, itwill be apparent to those skilled in the art that many othermodifications, as well as variations in the particular modificationsdescribed, are possible. For example, any suitable number of horns maybe provided in each row, either with the cellular type of Figs. 3 to 5or the other type shown in Figs. 6 to 9. It is also obvious that thenumber of horn rows, the rates of flare, the sizes of the horns, theangles of distribution, and the direction in which each horn or horn rowis oriented may be varied to suit the requirements of the particularauditorium or other space or enclosure where the loud speaker is to beused. In certain cases, it may be found desirable to use directradiators without horns in one or more of the horn rows in place of thehorns. Hence, wherever the term sound radiator is used in thisspecification, it is intended to mean either a direct radiator usedwithout a horn, or the horn itself, as the case may be. Also, in certaincases, it may be desirable to arrange the horns in juxtaposed relationinstead of in superposed relation, as in Figs. 6 and 8. Furthermore, inconnection with the modification shown in Figs. 6 to 8, the flare ofeach horn could be either the same or different, as may be mostsuitable, and a separate driver may be provided for each horn or layer,as shown by the separate drivers 4|, 43 and 45 of Fig. 9, all thedrivers being connected to and fed from a common signal source 41 andthe power delivered to each driver being either the same or difierentdepending upon the distribution required. Other variations will, nodoubt, readily suggest themselves to those skilled in the art. Itherefore desire that my invention shall not be limited except insofaras is made necessary by the prior art and by the spirit of the appendedclaims.

I claim as my invention:

1. In sound reproducing apparatus, a plurality of discrete hornsarranged in superposed relation with their axes angularly related toeach other in a comon plane, said horns thereby all facing in differentdirections, said horns each having an angle of distribution from side toside which is of different magnitude than that of any other of saidhorns, each of said horns expanding radially over its said distributionangle, and said horns all having substantially the same mouth and throatareas and substantially the same rate of flare and being adapted to befed from a common signal source.

2. The invention set forth in claim 1 characterized in that themagnitude of the angle of flare of each of said horns in said commonplane is different.

acsaose 3. The invention set forth in claim 1 characterized in that theaspect ratio of the respective mouth areas of said horns differs foreach horn.

4. The invention set forth in claim 1 characterized by the addition of athroat member, and characterized further in that the throat ends of therespective horns are all connected to said throat member whereby saidmember is common to all of said horns.

5. The invention set forth in claim 1 characterized in that the anglesbetween the axes of adjacent horns vary progressively, the angle betweenthe axes of the two lowermost horns being smallest, and the anglebetween the axes of the two uppermost horns being largest.

6. Sound reproducing apparatus according 'to claim 1 wherein said hornsare arranged pyramid fashion and are adapted to be located adjacent oneend of an auditorium, each of said horns in association with apreselected and different area of said auditorium, and the distributionangle for each horn corresponding to the angle subtended by the areaassociated therewith.

7. Sound reproducing apparatus according to claim 1 wherein said hornsare arranged pyramid fashion and are adapted to be located adjacent oneend of an auditorium, each of said horns in association with apreselected and different area of said auditorium, the distributionangle for each horn corresponding to the angle subtended by the 8 areaassociated therewith and said distribution angles being progressivelysharper from the lowermost to the uppermost of said horns.

JOHN E. VOLKMANN.

REFERENCES CITED The following references are of record in the file ofthis patent:

UNITED STATES PATENTS Number Name Date 1,384,612 Gray July 12, 19211,684,975 Slepian Sept. 18, 1928 1,768,226 Williams June 24, 19301,776,902 Harrison Sept. 30, 1930 1,812,878 Karnes July 7, 19311,825,166 Sullivan Sept. 29, 1931 1,871,531 Kellogg Aug. 16, 19321,934,932 Lindenberg Nov. 14, 1933 1,992,268 Wente Feb. 26, 19352,045,180 Douthwaite June 23, 1936 2,089,391 Marion Aug. 10, 19372,127,110 Farrand Aug. 16, 1938 2,135,610 Wente Nov. 8, 1938 2,174,163Olson Sept. 26, 1939 2,175,833 Farrand Oct. 10, 1939 FOREIGN PA'IE'NTSNumber Country Date 20,797 Great Britain 1900

